A technique for converting a BB (base band) signal or an IF (intermediate) signal to an RF (radio frequency) signal, or converting the RF signal to the BB signal or the IF signal using a mixer is widely used in a field of a wireless communication. However, a carrier leakage occurs in a real mixer.
The carrier leakage is a phenomenon where not only a product of an input signal and an LO signal transmitted from a local oscillator is transmitted to an output stage, but the LO signal is also leaked to the output stage. When the carrier leakage occurs, an unwanted noise component exists in an output of the mixer to degrade a signal-to-noise ratio.
Korean Patent Publication No. 2005-0066953 titled “APPARATUS FOR COMPENSATING DC OFFSET, I/Q GAIN AND PHASE IMBALANCE AND COMPENSATION SYSTEM EMBODYING THE SAME” filed by Electronics and Telecommunications Research Institute discloses a technology for compensating a carrier leakage of an up-conversion mixer. In accordance with the 2005-0066953 Publication, a signal level detector for detecting a signal level (I2+Q2) for an RF signal, an analog-to-digital converter for converting an output of the signal level detector to a digital signal, a DC offset detector for integrating a product of an output of the analog-to-digital converter and a sign of I and Q channels to detect a DC offset of each of the channels, and a DC offset compensator for receiving an output of the DC offset detector to compensate the DC offset are disclosed.
However, the technology disclosed in the 2005-0066953 publication has various disadvantages including that analog circuits such as the signal level detector and the analog-to-digital converter should be added and digital circuits such as the DC offset detector and the DC offset compensator should be added to a general tranceiving circuit that does not compensate the carrier leakage. Moreover, in accordance with the technology disclosed in the 2005-0066953 Publication, since the analog-to-digital converter converts an original transmission signal having a relatively high level to the digital signal as well as the DC offset having a relatively low level caused by the carrier leakage, a detection and a compensation of the DC offset are not facile or effective because of a noise (e.g., quantum noise) generated during the conversion.